Allow arity checks on dynamic function types

test/dart_codegen/expect/convert/json.dart

 part of dart.convert;
  class JsonUnsupportedObjectError extends Error {final unsupportedObject;
  final cause;
  JsonUnsupportedObjectError(this.unsupportedObject, {
   this.cause}
 );
  String toString() {
   if (cause != null) {
     return "Converting object to an encodable object failed.";
     }
@@ skipping 42 matching lines @@
 }
  JsonDecoder get decoder {
 if (_reviver == null) return const JsonDecoder();
  return new JsonDecoder(_reviver);
 }
 }
  class JsonEncoder extends Converter<Object, String> {final String indent;
  final Function _toEncodable;
  const JsonEncoder([Object toEncodable(Object nonSerializable)]) : this.indent = null, this._toEncodable = toEncodable;
  const JsonEncoder.withIndent(this.indent, [Object toEncodable(Object nonSerializable)]) : this._toEncodable = toEncodable;
- String convert(Object object) => _JsonStringStringifier.stringify(object, DEVC$RT.cast(_toEncodable, Function, __t9, "CastGeneral", """line 243, column 48 of dart:convert/json.dart: """, _toEncodable is __t9, false), indent);
+ String convert(Object object) => _JsonStringStringifier.stringify(object, DEVC$RT.cast(_toEncodable, Function, __t9, "CastGeneral", """line 243, column 48 of dart:convert/json.dart: """, _toEncodable is __t9, true), indent);
  ChunkedConversionSink<Object> startChunkedConversion(Sink<String> sink) {
 if (sink is! StringConversionSink) {
 sink = new StringConversionSink.from(sink);
 }
  else if (sink is _Utf8EncoderSink) {
 return new _JsonUtf8EncoderSink(sink._sink, _toEncodable, JsonUtf8Encoder._utf8Encode(indent), JsonUtf8Encoder.DEFAULT_BUFFER_SIZE);
 }
  return new _JsonEncoderSink(DEVC$RT.cast(sink, DEVC$RT.type((Sink<String> _) {
 }
 ), StringConversionSink, "CastGeneral", """line 262, column 33 of dart:convert/json.dart: """, sink is StringConversionSink, true), _toEncodable, indent);
@@ skipping 79 matching lines @@
  final Function _toEncodable;
  final StringConversionSink _sink;
  bool _isDone = false;
  _JsonEncoderSink(this._sink, this._toEncodable, this._indent);
  void add(Object o) {
 if (_isDone) {
 throw new StateError("Only one call to add allowed");
 }
  _isDone = true;
  ClosableStringSink stringSink = _sink.asStringSink();
- _JsonStringStringifier.printOn(o, stringSink, DEVC$RT.cast(_toEncodable, Function, __t9, "CastGeneral", """line 425, column 51 of dart:convert/json.dart: """, _toEncodable is __t9, false), _indent);
+ _JsonStringStringifier.printOn(o, stringSink, DEVC$RT.cast(_toEncodable, Function, __t9, "CastGeneral", """line 425, column 51 of dart:convert/json.dart: """, _toEncodable is __t9, true), _indent);
  stringSink.close();
 }
  void close() {
 }
 }
  class _JsonUtf8EncoderSink extends ChunkedConversionSink<Object> {final ByteConversionSink _sink;
  final List<int> _indent;
  final Function _toEncodable;
  final int _bufferSize;
  bool _isDone = false;
@@ skipping 387 matching lines @@
 }
 }
 }
 }
 }
  typedef Object __t7(Object __u8);
  typedef dynamic __t9(dynamic __u10);
  typedef dynamic __t13(Object __u14);
  typedef void __t21(String __u22, Object __u23);
  typedef dynamic __t24(String __u25, dynamic __u26);